Thousands of corpses of the footsoldiers who perished in Napoleon's disastrous 1812 retreat from Moscow have been discovered in a mass grave in the Lithuanian capital, Vilnius, offering a rich insight into the conditions and circumstances of history's most tragic military march.

Lithuanian archaeologists and French experts in forensic exhumation are poring over the remains of 2,000 young men of the imperial Grand Army who died of cold, hunger, disease and Russian retribution following the collapse of Napoleon's campaign on the scorched earth of Russia.

"This is a unique opportunity to prove some of the historical points about the retreat of the Grand Army," said Professor Olivier Dutour, a Marseilles university anthropologist who is in charge of the exhumation project. "We are looking directly at history."

The mass grave was discovered almost a year ago when building workers laying telephone lines at a former Soviet military base in Vilnius stumbled upon piles of bones in a 100sq-metre ditch.

Because of the area's association with the Red Army, it was instantly assumed that the corpses were of victims of communist or Nazi persecution from the 1940s or 50s. But fragments of buttons, clothing and other artefacts soon revealed that the dead were from 190 years ago when tens of thousands of Bonapartist troops passed through Lithuania in their flight from the Russians in December 1812.

"Not all the uniforms were French. There were also Portuguese, Italian, maybe Swiss, soldiers of perhaps 20 nationalities," said Olivier Poupard, charge d'affaires at the French embassy in Vilnius. "It's an exceptional discovery."

Exhumation

The cold weather last winter delayed exhumation and examination, but in recent months French and Lithuanian researchers have been examining skeletons, teeth and bone remnants from what is believed to be the biggest mass grave from the Napoleonic wars yet found in Europe.

The anthropologists and archaeologists have recovered the skeletons of more than 1,700 males, mainly aged between 15 and 25. In total, there were around 2,000 bodies buried en masse in the trench that Napoleon's men dug themselves to fortify Vilnius as the emperor gathered an army of 614,000 men to invade Russia six months earlier in June 1812.

It was a decision Napoleon came to rue. That army was destroyed. Of more than 614,000, only 50,000 survived. As with Hitler 130 years later, the Russia campaign proved the turning point leading to defeat in Europe. From Borodino outside Moscow to Waterloo took three years. Within four years of invading Russia in 1941, the Nazis were routed.

But Napoleon loved Vilnius which still boasts one of the most perfectly intact medieval city centres in Europe. Of the lovely late-Gothic church of St Anne's, the Emperor is said to have remarked: "If only I could, I would carry it back to Paris with my own hands."

Instead, routed by the Russians over several weeks, Napoleon abandoned his huge army and sped back to France escorted by a Lithuanian aide to whom he gave two pistols and ordered that he, Napoleon, should not be captured alive.

Ever since, historians have been divided over whether Napoleon made the weather an excuse for his defeat to cover up strategic and tactical blundering.

Prof Dutour says the Vilnius discoveries vindicate the diminutive megalomaniac. "The results confirm the extreme cold at this period. Napoleon claimed that he ordered the retreat because of the cold. And it's clear that some of the corpses really were frozen solid when they died in temperatures of -40C. It was like being in a deep freeze."

While the nationalities of the dead are not clear, it is assumed that the mass grave contained the remains of young men from all across Europe since the huge army assembled by Napoleon included Lithuanians as well as Poles, Germans, Austrians, Spanish, and Croats.

The Lithuanian and Polish aristocracies were quick to support Napoeleon's campaign against Russia since they detected an opportunity to recover their countries - which had been wiped off the map of Europe 17 years earlier in the partition by Russia, Prussia and Austro-Hungary.

But the pro-Napoleon hopes of the summer of 1812 quickly turned to despair, fear, and panic by the winter. Contemporaneous accounts provide graphic detail of the death and horror stalking the city as the remnants of the Grand Army took the Baltic route west.

Robert Wilson, a British officer attached to the Russian general staff, described the scene at a French military hospital in Vilnius: "The hospital presented the most awful and hideous sight: 7,500 bodies were piled up like pigs of lead over one another in the corridors. Carcasses were strewed about in every part; and all the broken windows and walls were stuffed with feet, legs, arms, hands, trunks and heads to fit the apertures, and keep out the air from the yet living."

The cold and hunger were exacerbated by the vengeance exacted by the Cossacks and Russian troops, who harried the retreating Napoleonic force and followed it into Vilnius.

The tsarist Polish prince Adam Czartoryski wrote to Tsar Alexander I of Russia complaining of the atrocities he witnessed: "You have no idea, Sire, of the evil that is being done in your name," he said. "The five Governments of Lithuania, instead of enjoying the benefits you wish to grant them, are suffering under an administration that is more unjust and arbitrary than any of those that have preceded it. No one's property, life or honour is safe."

The recovered remains are to be buried in a Vilnius cemetery, perhaps next month, although diplomatic and political considerations are delaying a decision. The French government has plans to supply a memorial.

The researchers intend to excavate elsewhere in Vilnius, expecting to locate a further 10,000 corpses from Napoleon's great defeat, although the French government does not look systematically for war dead from before 1870.

Analysis of the skeletons is providing much information on the diets, physical condition and illness at the beginning of the 19th century, says Prof Dutour.

"This was not a French army. It was a European army," he said. "So it gives us a chance to look at the condition of the population of Europe at the beginning of the 19th century."

·Huge blunder that sealed soldiers' fate

In what must rank as one of the greatest military miscalculations of all time, Napoleon Bonaparte crossed the River Niemen separating the French-controlled Duchy of Warsaw from Russian-controlled Lithuania on June 24 1812.

Tchaikovsky would later dedicate his famous overture to the year. Tolstoy devoted his longest novel, War and Peace, to the shattering events.

It is believed the Emperor headed the biggest army ever assembled at the time for a military campaign - 614,000 men of at least 20 different nationalities. Within six months at least nine out of 10 of them were dead.

The ostensible aim of the Russia invasion was to force Tsar Alexander I to join Napoleon's continental blockade of Britain. Napoleon's army was welcomed in Lithuania and Poland as liberators from the Russian despots who had gained control of most of both countries in 1795. Within three months and following the rout of the Russians at Borodino on the western approaches to Moscow, Napoleon was entrenched in the Kremlin. That was mid-September.

The Russians headed east, but not before torching their own city in an extravagant act of destruction that denied the Grand Army badly needed supplies and quarters.

Napoleon waited in Moscow for five weeks, expecting the tsar to capitulate and sign a peace treaty dictated by the French.

Then at the end of October he ordered the retreat from Russia, just as winter was setting in. That decision ultimately sealed his fate at Waterloo three years later.

The Grand Army troops died in their tens of thousands as they made their way west. It is reckoned that only 35,000 reached Vilnius on December 9, with as many having died in the previous four-day march to the undefended city.

The Russians arrived 24 hours later and vented their rage. But most of Napoleon's troops had died of cold, hunger, and disease by the time Tsar Alexander entered Vilnius on December 22.

The Emperor himself had already fled, abandoning his great army to the most tragic of fates.